The studio, which is owned by the 68-year-old fitness guru, hosted its final class on Saturday at 11:15 a.m.. Nearly 60 people, ages 25 to 94, attended, and according to an eyewitness, some came as far as Toronto and San Francisco to get one last hour-long workout in at the iconic location.

"The room was filled with a lot of emotion, but you felt the spirit of Richard within the room while we were here," the eyewitness told ET.

Another person in class said the workout "went beautifully," and concluded with a brief stretch to Rascal Flatts' "My Wish."

"It was hard," they added. "It was just like Richard taught them to be and all of us to enjoy."

Although Simmons did not make an in-person appearance on Saturday, he did offer a heartfelt message to those in attendance via a note read aloud by the studio manager. In the letter, Simmons thanked his loyal members who have been attending for years, along with those who came for their first time.

"It felt like he put a period at the end of the sentence," a young female in attendance explained to ET. "I'm glad to know he's doing well."

"He will always be a gift to me," another fan shared. "I will never, never forget him."

Simmons later shared the exact note to his Facebook page. "I have never been very good with beginnings and endings," he began. "This may come as a surprise to some of you, but I am not the most patient person. I just can't wait for a movie to start, or a new restaurant or business to open, or for class to begin. Hurry up already!"

"When I opened Slimmons in 1974," he continued, "I simply couldn't wait to tell everyone that food could be healthy AND delicious or that exercise could be fun! I worked my little striped shorts off to spread the message that you must move your body every day, that portion size matters and that while others may not always be kind to you, you must be kind to yourself. I traveled the country, appeared in malls and convention halls, talk shows, news segments and made more guest appearances than I can name. I made countless friends along the way and I hope I changed a few lives for the better."

"Well, it's been over forty years now, and I am finally taking my own advice," Simmons, who said he was not in attendance for the last class because he is "not very good at endings," added. "I am being kind to myself, and putting myself first. I am making changes and taking time to do the things I want to do. Please know that I am in good health and I am happy. No one has ever been able to tell me what to do and the same is true today. I am still independent, determined and opinionated. I simply am making a new beginning for myself -- quietly and in my very own special way."

"I cannot bear to be sad today. And you shouldn't be sad either," he urged his fans. "This should be a celebration of our forty-plus years together dancin' and sweatin'. So let's turn this ending into a new beginning. Start your own chapter today. Do something new you've always wanted to do. Make a new friend. Exercise. Eat a healthy meal. Drink water. Track your food. Spend time with your family or the ones you love and those who love you back. But most importantly be good to yourself."

Simmons' longtime manager, Michael Catalano, confirmed the news that the studio was closing last month, telling ET it was Simmons' idea to close it for good and that "he just hasn't taught there in over two years."

On Friday, Simmons further explained his decision in an exclusive statement to ET.

"In 1974, I opened Slimmons as a way to help people make positive changes in their lives by having fun while exercising," he said. "It was a place to make friends, listen to and learn from others, lose weight and gain confidence. These were all the reasons I went to Slimmons too!"

"Over the years, thousands came to laugh and sweat with me," he added. "The world and what we know about nutrition and fitness may have changed a lot since then, but the lessons shared in that little studio still apply. I've dedicated my life to helping others feel better about themselves, and they helped me to do the same. Thank you for always supporting and loving me. I will take the time for myself to be the best I can be and so should you. I love you -- always keep sweatin'!"